The invention relates to ratchet mechanisms that drive rotational movement, and more particularly to an improvement in a ratchet actuator that is driven by air drivers such as might be used in a landing gear of a semi-trailer.
One environment to which the invention may be applicable is found in FIG. 1 where a conventional landing gear 10 for a semi-trailer is shown. The landing gear 10 is used to support a semi-trailer when the semi-trailer is disconnected from a tractor. The landing gear 10 is designed to expand and contract vertically. In expansion, the landing gear 10 lifts the front of a semi-trailer so that it can be disconnected from the tractor, and thereafter supports the front of the semi-trailer when the tractor departs. In contraction, the landing gear 10 lowers the front of the semi-trailer to enable connection to a tractor, and, once connected, to further gain ground clearance so the semi-trailer can be pulled by the tractor free of interference.
The landing gear 10 comprises a pair of spaced arms 12, each having a mounting bracket 14 for securing the landing gear to a frame of a semi-trailer (not shown). Each arm 12 comprises a hollow tube 16 within which is a leg that is geared to extend from and retract into the hollow tube 16. Each leg has a foot pad 18 that supports the landing gear 10 on the ground. A gearbox 20 mounted to one of the arms controls the extension and retraction of both legs by way of a cross drive shaft 22 extending between the arms 12. The gearbox 20 is manually driven by a crank handle 24. It can require substantial torque via the gearbox 20 to raise a loaded semi-trailer, on the order of approximately 100 foot pounds.
It is known to use pneumatic assist for a landing gear on a semi-trailer. U.S. Pat. Nos. 4,402,526 and 4,400,986 disclose a pneumatically operated actuator with a complex system of gears and ratchets. U.S. Pat. No. 4,116,315 discloses a pneumatically operated actuator with a complex clutch mechanism. There reminds a need for a simpler, lower cost actuator that can be applied to existing systems retroactively without undue modification.